Steering columns for motor vehicles are designed to collapse longitudinally through an energy absorbing stroke in response to an impact on the steering column. For example, in a frontal collision, a driver's chest may impact the steering wheel, causing an axial force along the steering column. The connection which holds the steering column to the motor vehicle body is designed to release in a collision to prevent or reduce injury to the driver's chest.
One typical method of accomplishing this releasable connection is to provide a support bracket on the outer, non-rotating sleeve of the steering column. The support bracket is designed with a releasable mounting surface. A release capsule, in turn, is fixed to the vehicle body and engages the mounting surface of the support bracket in such a manner that, upon the application of sufficient force along the longitudinal axis of the column sleeve, the connection is overcome thus allowing the steering column to collapse along its length. An energy absorbing mechanism may be incorporated into the connection between the release capsule and the support bracket to help control, or dampen, the relative movements.
Although many releasable connection designs and mechanisms have been proposed, a kind frequently employed includes the use of plastic injection-molded sheer pins which pass between the release capsule and the support bracket. Upon the application of sufficient force, these sheer pins yield allowing the support bracket to disengage from the fixed release capsule. While this sheer pin technique is reliable, there are nevertheless certain inherent characteristics of this design which could be improved upon. For example, it would be beneficial to improve the predictability of the release force at which the connection between the release capsule and the support bracket is overcome. That is, because plastic sheer pins can be subject to manufacturing variables, such as injection temperature, injection pressure and spatial clearance between the components, the exact release force necessary to disengage the support bracket from the release capsule can vary from one vehicle to the next. Another example of a characteristic which could be improved relates to engine vibrations transmitted through the steering column to the steering wheel. Because the support bracket and release capsule connection is the mechanism by which the steering column is supported to the vehicle body, vibrations transmitted through the vehicle body pass through this connection to the steering column. The plastic material present in prior art release capsule designs has an inherent softness which can raise the frequency value of the column. This can, in certain circumstances, result in vibrations transmitted to the steering wheel which can be felt by a driver.
Therefore, there is a need to improve release connections for vehicular steering columns for the purpose of providing greater predictability in the release force and lowering the frequency value of the steering column assembly.